The present invention relates to technique of controlling a valve timing of an intake valve and/or an exhaust valve of an internal combustion engine.
A Published Japanese Patent Application Publication No. H11(1999)-141313 shows a valve timing control system including a first operating mechanism for varying the rotational phases of intake and exhaust camshafts simultaneously, and a second operating mechanism for varying the rotational phase of one of the intake and exhaust camshafts. The shift of a rotational phase is achieved by advancing or retarding the phase with respect to the rotational direction of each camshaft. This angle is referred to as a valve timing control conversion angle.